The present invention relates to a flight control device for an aircraft, in particular for a helicopter.
This device which, within the context of the present invention, may be a device of the type having mechanical or electric flight controls comprises, in a known manner, for control with respect to at least one of the roll and pitch control axes considered in the present invention:
at least one control member (stick or ministick) capable of being actuated by a pilot of the aircraft;
at least one means of actuation (servocontrol) of a controlled member (rotor), to which a control command is applied; and
means of determination for determining and transmitting to said means of actuation a control command dependent on an actuation value representative of the actuation of said control member.
Consequently, when the pilot of the aircraft actuates the roll or pitch control member, that is to say brings about a deflection of said control member, the means of determination determine, according to a predetermined control law, a control command, for example an angular rate control command, which is dependent on this deflection.
It is known that an angular rate control of the xe2x80x9cRCxe2x80x9d (xe2x80x9cRate Commandxe2x80x9d) type, for which the deflection (longitudinal in the case of pitch or lateral in the case of roll) of the control member directly controls an angular rate of pitch or of roll about the relevant axis of the aircraft, proves to be especially well suited to maneuvers of large amplitude.
Of course, other types of control laws are known. In particular, control laws which implement:
a translational rate control of the xe2x80x9cTRCxe2x80x9d xe2x80x9cTranslational Rate Commandxe2x80x9d) type, for which a longitudinal or lateral deflection of the control member or stick directly controls a longitudinal or lateral translational rate along the axis (of pitch or roll), which proves to be especially well suited for the hovering or low-speed phases, close to the ground or to obstacles, and in particular under conditions of degraded visibility; and
a translational acceleration control of the xe2x80x9cAcCxe2x80x9d (xe2x80x9cAcceleration Commandxe2x80x9d) type, for which a longitudinal or lateral deflection of the stick directly controls a longitudinal or lateral translational acceleration along the axis (this being very similar in fact to the direct control of pitch or roll attitude about the axis), which proves to be especially well suited for the cruising flight phases, and in particular for the tactical flight phases.
However, irrespective of the relevant control axis (roll or pitch) and irrespective of the type of aircraft used, it is not possible to simultaneously employ, or even to combine, various types of control (angular rate control, translational rate control or translational acceleration control). Consequently, irrespective of the control used, there are always flight phases for which this control is hardly appropriate.
By way of illustration, it will be recalled that:
in helicopters having mechanical flight controls, not fitted with an automatic pilot, the dynamic pitch or roll response is naturally of the xe2x80x9cRCxe2x80x9d (angular rate) type;
in helicopters having mechanical flight controls, fitted with an automatic pilot, the dynamic pitch or roll response is generally again of the xe2x80x9cRCxe2x80x9d (angular rate) type, since the authority of the control system is too little to be able to modify the response; and
in helicopters having electric flight controls with so-called xe2x80x9cobjective-basedxe2x80x9d control laws, the type of the response may be modified into the xe2x80x9cTRCxe2x80x9d (translational rate) type or xe2x80x9cAcCxe2x80x9d (translational acceleration) type.
The present invention relates to a (mechanical or electric) flight control device for an aircraft, in particular for a helicopter, which makes it possible to remedy the aforesaid drawbacks.
For this purpose, according to the invention, said flight control device for an aircraft, of the type comprising for control with respect to at least one control axis:
at least one control member capable of being actuated by a pilot of the aircraft which produces a deflection of said control member;
at least one means of actuation of a controlled member to which a control command is applied; and
means of determination for determining and transmitting to said means of actuation a control command dependent on an actuation value representative of the actuation of said control member,
is noteworthy in that it comprises, moreover, at least one first sensor for determining a first effective value corresponding to the effective value of the translational rate of the aircraft, and in that said means of determination are formed in such a way as to determine as control command to be applied to said means of actuation:
while said first effective value is less than or equal to a first reference value corresponding to a predetermined reference value of the translational rate, a first control command corresponding to a translational rate control command, which is dependent on the deflection of the control member; and
when said first effective value is greater than said first reference value, at least one second control command, which is different from a translational rate control command and which is dependent on an extra deflection of the control member.
Thus, by virtue of the invention:
while the translational rate is small (namely less than the first reference value), the aircraft is controlled by a translational rate control (TRC), which, as is known, proves to be especially well suited for the hovering or low-speed phases, close to the ground or to obstacles, and in particular under conditions of degraded visibility, that is to say for low speeds; and
when the speed becomes greater, the aircraft is controlled according to at least one other type of control, as specified hereinbelow, which is different from a translational rate control and which is suited to high speeds, thereby making it possible to remedy the fact that a translational rate control exhibits a small flight domain (defined around a reference rate) which is no longer suited to the higher speeds, considered in the present case.
In a first embodiment, said second control command is a translational acceleration control command (AcC), which is dependent on the extra deflection beyond the deflection producing a translational rate which is equal to said first reference value.
In a second embodiment, said second control command is an angular rate control command (RC), which is dependent on the extra deflection beyond the deflection producing a translational rate which is equal to said first reference value.
Thus, an advantageous compromise is obtained between a control law (TRC law) suitable for carrying out precision maneuvers and a control law (RC law) which is sufficiently maneuverable to cover all of the flight domain.
In a third preferred embodiment, said device furthermore comprises at least one second sensor for determining a second effective value corresponding to the effective value of the translational acceleration of the aircraft, and said means of determination are formed in such a way as to determine as second control command:
while said second effective value is less than or equal to a second reference value corresponding to a predetermined reference value of the translational acceleration, a translational acceleration control command, which is dependent on the extra deflection beyond the deflection producing a translational rate which is equal to said first reference value; and
when said second effective value is greater than said second reference value, an angular rate control command, which is dependent on the extra deflection beyond the deflection producing a translational acceleration which is equal to said second reference value.
Thus, the three types of control (TRC, AcC, RC) are combined. Moreover, each control is rendered active in the flight domain where it is most efficacious, thereby making it possible to marry the advantages of said three controls.
For this purpose, in addition to the aforesaid advantages of translational rate control (TRC), it is known that:
translational acceleration control (AcC) which covers a more extensive flight domain and makes it possible to manage rate deviations (possibility of accelerating and of decelerating) is especially well suited to the cruising flight phases, in particular the tactical flight phases; and
angular rate control (RC) which covers a broad flight domain is especially well suited to dynamic maneuvers of large amplitude (that is to say for high translational rates and translational accelerations).
In a fourth particular embodiment, said flight control device for an aircraft, in particular for a helicopter, of the type comprising for control with respect to at least one control axis:
at least one control member capable of being actuated by a pilot of the aircraft which produces a deflection of said control member;
at least one means of actuation of a controlled member to which a control command is applied; and
means of determination for determining and transmitting to said means of actuation a control command dependent on an actuation value representative of the actuation of said control member,
furthermore comprises at least one sensor for determining an effective value of the translational acceleration of the aircraft, and said means of determination are formed in such a way as to determine as control command to be applied to said means of actuation:
while said effective value is less than or equal to a predetermined reference value of the translational acceleration, a translational acceleration control command, which is dependent on the deflection of the control member; and
when said effective value is greater than said reference value, an angular rate control command, which is dependent on the extra deflection beyond the deflection producing a translational acceleration which is equal to said reference value.
Of course, the flight control device in accordance with the invention may be applied equally well to control with respect to the roll control axis as to control with respect to the pitch control axis.
Moreover, in a particular embodiment, said device comprises control members, means of actuation, sensors and means of determination for controlling the aircraft with respect to each of the roll and pitch control axes of said aircraft.
The figures of the appended drawing will elucidate the manner in which the invention may be embodied. In these figures, identical references designate similar elements.